K&N filters are snake oil for the reasons mentioned above. Get some quality dry filters and be done.
As for your CEL, I suspect either the MAF sensor got oil on it, or you inadvertently changed the inside diameter of the intake tubes by removing the sleeves. Im not sure if these have sleeves in...
There are valves that open inside the mufflers. Track mode simply means the valves are all the way open so the chambers have maximum flow. I certianly don't interpret that to be the same as a muffler delete.
The Cobra and fox guages are just a novelty to me. I don't use them since they don't have a digital speed readout. Plus, it seems a little odd to have throwback guages with a flat screen and modern interior.
Seems. Easy enough. I'll get the cable and give it a try.
Is the seat belt display when you start the car something you can disable in easy mode by chance?
No it does not fit over the existing spoiler. The old one has to be removed.
Bring a friend and lots of tape when you put the new one on. It's difficult to align correctly and once the double sided tape makes contact there is no adjusting.
I'd really like to see a walk through on how to this for 5 year olds. There is so much info scattered around, and most of it starts way over my head. 😆